What are the advantages of using transistor as an switch instead of diode?

1. A transistor *is* a triode- this is the general name for any three-electrode electronic device.

2. Most people understand "triode" to mean a tride vacuum tube/valve.

3. The transistor

(i) needs no heated filament/cathode, so it uses much less power than a valve triode,

(ii) because of (i), transistors do not "burn out" with age, so they have much longer lifetimes, are much more reliable, and generate much less waste heat,

(iii) transistors can operate at much lower power than triode valves, and at much higher frequencies,

(iv) transistors can be made much smaller than triodes, by a factor of many tens of thousands,

(v) from early on, transistors were much cheaper than triode valves.